Rotatable base for an umbrella



FIG. 1 is a top view of the rotatable base for an umbrella showing my new design;

FIG. 2 is a bottom view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a back view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a right side view thereof; and,

FIG. 7 is a top perspective view thereof.

The broken lines in the figures are for the purpose of illustrating portions of the rotatable base for an umbrella, which form no part of the claimed design. 

CLAIM The ornamental design for a rotatable base for an umbrella, as shown and described. 